448 Significance HIV is primarily a sexually transmitted disease but little is known about the transmission of viral variants during sexual contact. Development of a women-controlled methods for preventing sexual HIV transmission is a critical need for reducing the impact of AIDS on women and children, especially in developing countries. Objectives In this study, we used the rhesus macaque/SIV model to test the efficacy of a proprietary carbohydrate compound based on carrageenans. Carrageenans are used to make ice cream smooth. Results Four mature female rhesus macaques were treated by placing 1 ml of the compound in the vagina. After waiting 5 minutes, 1 ml of SIVmac251 was placed into the vagina. This treat and challenge procedure was repeated once. The animals were monitored for SIV infection for 4 months. Two of 4 animals were protected from SIV infection by the compound. This positive result suggests that very safe, non-irritating compounds will be useful for preventing HIV transmission. Future Directions The collaborator is attempting to produce a compound with higher efficacy. KEY WORDS microbicides, HIV mucosal transmission FUNDING Population Council